End stage renal disease currently affects over 100,000 patients in the United States, and over 400,000 patients worldwide. The patient load for this disease continues to grow at a seven percent annual rate.
Kidney failure may be acute or chronic. Acute failure may be caused by trauma, surgery, or disease but is time-limited as the patient heals. Chronic failure is permanent and will continue for the long term until the patient dies. Treatment for chronic or end stage renal disease consists of kidney transplant procedures or dialysis. Kidney transplant therapy is limited by the availability of suitable organ donors, and dialysis becomes the only remaining treatment for chronic kidney failure.
Dialysis is the process of removing metabolic waste products from the blood, a function performed by the natural kidney in a healthy condition. These waste products include salts, urea, creatinine, uric acid, and water. The substances are removed by diffusion across a membrane to a dialysate fluid which has a low concentration of the substances.
Dialysis takes place either by continuous ambulatory peritoneal dialysis in which the membrane used is the vascular membranes of the body in the peritoneal cavity, or hemodialysis in which an artificial membrane is used. In hemodialysis, blood is removed from an artery or vein, passed over one side of an extracorporeal porous dialyzer membrane is used. In hemodialysis, blood is removed from an artery or vein, passed over one side of an extracorporeal porous dialyzer membrane, and returned to the body via a vein. The membrane is made of cellulous or another suitable material. Dialysate fluid is passed over the other side of the dialyzer membrane and the metabolic waste products pass through the porous membrane from the blood to the dialysate by the process of diffusion. The pores in the membrane are sized such that the waste products pass through the membrane but other blood components such as hemoglobin, albumin, gamma globulin, virus and bacterial bodies, are too large and cannot pass through the pores. Excess water is passed through the membrane by an ultrafiltration process in which a positive pressure gradient is created between the blood and the dialysate on opposite sides of the membrane.
Although hemodialysis is widely used as a treatment for chronic kidney failure, there are significant problems associated with that procedure. For one, the removal of whole blood from the body, followed by processing and returning that blood, causes clotting, infection, and damage to the cells, as well as damage to proteins and other blood components.
The batch-treatment orientation of hemodialysis represents another problem. Current hemodialysis therapy methods are high velocity, high volume batch processes where the total blood volume of a patient is removed, dialyzed, and returned in a single treatment session which may last three to four hours. These treatment sessions take place several times each week. Because the generation of toxic metabolic waste by the body is continuous, this waste will build up to unacceptable concentrations in the blood between dialysis sessions. Furthermore, the massive blood removal and constituent changes during a dialysis session cause cardiovascular trauma as well as nausea and other systemic disorders.
Patient immobility is yet another problem of present hemodialysis methods. Because of the large volume, high flow requirements of present hemodialysis systems, the apparatus is large and heavy and the patient thus is immobilized for the time that the procedure requires.